High-resolution calorimetric absorption measurements on optical components for excimer lasers

In the past, we presented several works showing that laser calorimetry can be applied in the W-spectral range with greatly enhanced sensitivity compared to transmission measurements. We have now finished developing an improved laser calorimeter which is two orders of magnitude more temperature sensitive than our previous setup. This added resolution can be employed to measure absorptance as a function of irradiation parameters such as energy density or pulse repetition rate over an even broader range. In particular; the irradiation energy dose per measurement can be kept low enough to allow cumulative laser-induced absorption increase to be monitored with very high (eventually single pulse) resolution. We used the new setup to cast some light on the scaling laws of absorptance in fused silica as a function of the sample thickness. It was possible to distinguish between surface and bulk processes.